Apparatus, device and method that enable efficient reference signal placement and acquires feedback information

ABSTRACT

A communication system where a terminal apparatus (UE) communicates with a base station apparatus (BS) that configures a first cell. The UE acquires, from the BS, first information and second information, whereby the first information specifying a first number indicating a first subframe, the first subframe including a first resource element in which a first reference signal of the first cell is placed, the second information specifying a second number indicating a second subframe, the second subframe including a second resource element in which a second reference signal of a second cell other than the first cell is to be placed, and the second resource element being not used to transmit a signal of the first cell. The UE also demaps data, whereby, in the second subframe, the data is mapped on resource elements which do not include the second resource element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending application Ser. No.14/288,191 filed on May 27, 2014, which is a Continuation of applicationSer. No. 13/378,017 filed on Dec. 13, 2011, now U.S. Pat. No. 8,744,290issued on Jul. 8, 2014, and which is the national phase of PCTInternational Application No. PCT/JP2010/003632 filed on May 31, 2010,which claims priority under 35 U.S.C. 119(a) to Japanese Application No.2009-142873, filed in Japan on Jun. 16, 2009. The entire contents ofeach of the above-identified applications are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a transmitter apparatus, a receiverapparatus, a communication system, and a communication method.

BACKGROUND ART

Known mobile wireless communication systems include those such as WCDMA(Wideband Code-Division Multiple Access), LTE (Long Term Evolution),LTE-A (LTE-Advanced) and WiMAX (Worldwide Interoperability for MicrowaveAccess), in accordance with 3GPP (Third Generation Partnership Project).In these mobile wireless communication systems, an area that is coveredby a base station (base station apparatus, transmitting station,transmitter apparatus, eNodeB) or a transmitting station that is inaccordance with a base station has a cellular configuration in which aplurality of cells are disposed, thereby enabling an expansion of thecommunication area.

By using different frequencies between adjacent cells or betweenadjacent sectors, even for terminal devices (receiver apparatuses,receiving stations, mobile stations, mobile terminals, UE (userequipment)) in a cell edge region or a sector edge region, it ispossible to perform communication without interference from thetransmitted signals from a plurality of base stations. In this case,however, there is the problem of a poor rate of frequency spectrumutilization. By using the same frequency between adjacent cells orsectors, it is possible to improve the rate of frequency spectrumutilization. In this case, however, interference countermeasures arenecessary to handle interference to terminal devices positioned in acell edge region.

A method of suppressing interference with respect to terminal devices ina cell edge region by performing cooperative communication betweencells, in which there is mutual cooperation between adjacent cells isunder study as such an interference countermeasure. As such a method,Non-Patent Document 1 discloses a CoMP (Cooperative Multipoint) transfersystem (cooperative communication system) and the like. As the CoMPsystem, disclosure is made of joint processing, in which cooperativetransmission is done of the same or different data between cells, jointtransmission, coordinated scheduling, in which scheduling andcontrolling is done by coordination between cells, and beamforming.

By performing adaptive control of the modulation method, the codingscheme (MCS: Modulation and Coding Scheme), the spatial multiplexing(layers and ranks) and precoding weight (precoding matrix) in accordancewith the transfer status between a base station and a terminal device,it is possible to achieve data transfer with improved efficiency.Non-Patent Document 2 discloses a method that applies these types ofcontrol.

FIG. 17 is a drawing that shows a base station 1701 and a terminaldevice 1702 that perform non-cooperative communication (non-CoMP) with,for example, MIMO (multiple-input multiple-output) transmission from asingle cell in LTE-A. A proposal is made of the terminal device 1702 inLTE-A using a reference signal (RS) transmitted from the base station1701, a pilot signal, a known signal, and a propagation channel statusmeasurement reference signal, the CSI-RS (Channel State Information RS)to transmit feedback information to the base station 1701. The referencesignal is transmitted to the terminal device 1702 from the base station1701.

The terminal device 1702 transmits feedback information generated basedon the reference signal to base station 1701. In the case of thedownlink used for data transfer from the base station 1701 to theterminal device 1702, in order to perform the above-noted adaptivecontrol, the downlink propagation channel status or the like isestimated at the terminal device 1702 based on the reference signaltransmitted from the base station 1701. Then, estimated propagationchannel status or the like is transmitted (fed back) to the base station1701 via the uplink that performs data transfer from the terminal device1702 to the base station 1701. Non-Patent Document 3 proposes theplacement of a reference signal in only some of the subframes, ratherthan locating the reference signal in all subframes on the time axiswhen locating the reference signal.

FIG. 18 is a drawing showing an example of a reference signaltransmitted to the base station 1701. In FIG. 18, the horizontal axisindicates time and the vertical axis indicates frequency. The varioussquare regions within a resource block (RB) 1801 that is defined by aprescribed time and frequency indicate resource elements (this indicatesthe region in which the modulating symbol is mapped REs). The referencenumerals 1801-1 to 1801-4 indicate resource elements onto which theLTE-A reference signal is mapped. The reference numeral 1801-5 indicatesthe resource element onto which the LTE reference signal is mapped.

The reference numeral 1801-6 indicates a resource element onto which asignal other than the reference signal (that is, a data signal orcontrol signal or the like) is mapped. As the position of the referencesignal, it is possible to use a reference signal scattered among theresource elements in the frequency direction and the time direction. TheUE in the LTE-A system can use information that indicates the channelcharacteristics (CSI: Channel State Information), the recommendedtransmission format information with respect to the base station (CQI:Channel Quality Indicator), and the RI (Rank Indicator) and PMI(Precoding Matrix Index) as the information (feedback information) tothe base station, which is generated based on this LTE-A referencesignal.

FIG. 19 is a drawing showing a base station 1901, a base station 1902,and a terminal device 1903 that perform CoMP communication in the LTE-Asystem. A proposal has been made for the terminal device 1903 using thereference signals transmitted from each of the base stations 1901 and1902 to generate feedback information, and transmitting the generatedfeedback information to the base station 1901 in the LTE-A system. InNon-Patent Document 4, there is a proposal for puncturing data from thebase station 1902 at the terminal device 1903 when the reference signalis transmitted from the base station 1901, for the purpose of measuringthe reference signal with high accuracy when performing CoMPcommunication in the LTE-A system (that is, data is not mapped onto theresource element, or data transmission is stopped).

PRIOR ART DOCUMENTS Non-Patent Document

-   Non-Patent Document 1: 3rd General Partnership Project; Technical    Specification Group Radio Access Network; Further Advancements for    E-UTRA Physical Layer Aspects (Release X), January 2009, 3GPP TR    36.814 V0.3.2 (2009-01)-   Non-Patent Document 2: 3rd General Partnership Project; Technical    Specification Group Radio Access Network; Evolved Universal    Terrestrial Radio Access (E-UTRA); Physical Layer Procedures    (Release 8), December 2008, 3GPP TS 36.213 V8.5.0 (2008-12)-   Non-Patent Document 3: 3GPP TSG RAN WG1 #56-bis, R1-091351, “CSI-RS    design for LTE-Advanced downlink”, March 2009-   Non-Patent Document 4: 3GPP TSG-RAN WG1 #56, R1-090875, “Further    Considerations and Link Simulations on Reference Signal in LTE-A”,    February 2009

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In conventional communication schemes, however, in a communicationsystem capable of non-cooperative communication and cooperativecommunication, it is difficult to efficiency place the reference signaland difficult to acquire appropriate feedback information, thishindering improvement in the transfer efficiency.

The present invention was made in consideration of the above-notedproblems, and has as an object to provide a transmitter apparatus, areceiver apparatus, a communication system, and a communication methodthat, in a communication system capable of non-cooperative communicationand cooperative communication, enable efficient reference signalplacement and the acquisition of appropriate feedback information.

Means for Solving the Problem

(1) The present invention has been made to solve the above-describedproblems, and a first aspect of the present invention is a transmitterapparatus including: a reference signal transmitting unit that transmitsa both of a first reference signal and a second reference signaldiffering from the first reference signal to a first receiver apparatusperforming non-cooperative communication and to a second receiverapparatus performing cooperative communication, respectively; and anotifying unit that instructs the first receiver apparatus to measurethe first reference signal and that instructs the second receiverapparatus to measure the second reference signal.

(2) In the first aspect of the present invention, the transmitterapparatus may further include a first mapping unit that maps the firstreference signal and the second reference signal onto differentresources.

(3) In the first aspect of the present invention, the first mapping unitmay use the same stream as the first reference signal and the secondreference signal.

(4) In the first aspect of the present invention, the transmitterapparatus may further include a second mapping unit that places thefirst reference signal and the second reference signal onto differentsubframes.

(5) A second aspect of the present invention is a transmitter apparatusincluding: a reference signal transmitting unit that transmits a both ofa first reference signal and a second reference signal differing fromthe first reference signal to a first receiver apparatus performingnon-cooperative communication and to a second receiver apparatusperforming cooperative communication, respectively; and a notifying unitthat notifies of information specifying a position of the firstreference signal to the first receiver apparatus, and that notifies ofinformation specifying a position of the second reference signal to thesecond receiver apparatus.

(6) A third aspect of the present invention is a receiver apparatusincluding: a first reference signal measuring unit that measures a firstreference signal based on the instruction of measurement of the firstreference signal from a transmitter apparatus performing communicationby switching between non-cooperative communication and cooperativecommunication; and a second reference signal measuring unit thatmeasures a second reference signal differing from the first referencesignal based on the instruction of measurement of the second referencesignal from the transmitter apparatus.

(7) In the third aspect of the present invention, the receiver apparatusmay further include: a first feedback information generating unit thatgenerates first feedback information using a measurement result of thefirst reference signal; and a second feedback information generatingunit that generates second feedback information differing from the firstfeedback information using a measurement result of the second referencesignal.

(8) A fourth aspect of the present invention is a communication systemincluding a transmitter apparatus and a first and second receiverapparatuses, wherein the transmitter apparatus includes: a referencesignal transmitting unit that transmits both of a first reference signaland a second reference signal differing from the first reference signalto the first receiver apparatus performing non-cooperative communicationand to the second receiver apparatus performing cooperativecommunication, respectively; and a notifying unit that instructs thefirst receiver apparatus to measure the first reference signal and thatinstructs the second receiver apparatus to measure the second referencesignal; and wherein the first receiver apparatus includes: a firstreference signal measuring unit that measures the first referencesignal; and the second receiver apparatus includes: a second referencesignal measuring unit that measures the second reference signal.

(9) A fifth aspect of the present invention is a communication systemincluding a transmitter apparatus and a receiver apparatus, wherein thetransmitter apparatus includes: a reference signal transmitting unitthat transmits a first reference signal and a second reference signaldiffering from the first reference signal to the receiver apparatusperforming communication by switching between non-cooperativecommunication and cooperative communication; and a notifying unit thatinstructs the receiver apparatus to measure the first reference signalor to measure the second reference signal; and wherein the receiverapparatus includes: a first reference signal measuring unit thatmeasures the first reference signal based on the instruction to measurethe first reference signal from the transmitter apparatus; and a secondreference signal measuring unit that measures the second referencesignal based on the instruction to measure the second reference signalfrom the transmitter apparatus.

(10) A sixth aspect of the present invention is a communication methodfor transmitting the both of a first reference signal and a secondreference signal differing from the first reference signal from atransmitter apparatus to a first receiver apparatus performingnon-cooperative communication and to a second receiver apparatusperforming cooperative communication, respectively, wherein thetransmitter apparatus instructs the first receiver apparatus to measurethe first reference signal; and the transmitter apparatus instructs thesecond receiver apparatus to measure the second reference signal.

(11) A seventh aspect of the present invention is a communicationmethod, wherein a receiver apparatus measures a first reference signalbased on the instruction to measure the first reference signal from atransmitter apparatus performing communication by switching betweennon-cooperative communication and cooperative communication; and thereceiver apparatus measures a second reference signal differing from thefirst reference signal based on the instruction to measure the secondreference signal from the transmitter apparatus.

Effects of the Invention

According to the present invention, it is possible in a communicationsystem capable of non-cooperative communication and cooperativecommunication, to efficiently place the reference signal and to acquireappropriate feedback information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing the configuration of acommunication system according to a first embodiment of the presentinvention.

FIG. 2 is a schematic drawing showing the configuration of thecommunication system in the same embodiment.

FIG. 3A is a drawing showing an example of the configuration of thereference signal in the same embodiment.

FIG. 3B is a drawing showing another example of the configuration of thereference signal in the same embodiment.

FIG. 3C is a drawing showing yet another example of the configuration ofthe reference signal in the same embodiment.

FIG. 4A is a drawing showing an example of the configuration of thereference signal in the same embodiment.

FIG. 4B is a drawing showing another example of the configuration of thereference signal in the same embodiment.

FIG. 4C is a drawing showing yet another example of the configuration ofthe reference signal in the same embodiment.

FIG. 5 is a drawing showing an example of the configuration of wirelessframes in the same embodiment.

FIG. 6 is a sequence diagram showing an example of the processingbetween a base station (transmitter apparatus) and a terminal device(receiver apparatus) in the same embodiment.

FIG. 7 is a simplified block diagram showing an example of theconfiguration of a base station (transmitter apparatus) in the sameembodiment.

FIG. 8 is a simplified block diagram showing an example of theconfiguration of the terminal device (receiver apparatus) in the sameembodiment.

FIG. 9A is a drawing showing an example of the configuration of thereference signal in a second embodiment of the present invention.

FIG. 9B is a drawing showing another example of the configuration of thereference signal in the second embodiment of the present invention.

FIG. 9C is a drawing showing yet another example of the configuration ofthe reference signal in the second embodiment of the present invention.

FIG. 10 is a drawing showing an example of the configuration of wirelessframes in the same embodiment.

FIG. 11 is a sequence diagram showing an example of the processingbetween the base station (transmitter apparatus) and the terminal device(receiver apparatus) in a third embodiment of the present invention.

FIG. 12 is a sequence diagram showing an example of the processingbetween the base station (transmitter apparatus) and the terminal device(receiver apparatus) in a fourth embodiment of the present invention.

FIG. 13 is a sequence diagram showing an example of the processingbetween the base station (transmitter apparatus) and the terminal device(receiver apparatus) in a fifth embodiment of the present invention.

FIG. 14 is a sequence diagram showing an example of the processingbetween the base station (transmitter apparatus) and the terminal device(receiver apparatus) in a six embodiment of the present invention.

FIG. 15A is a drawing showing an example of the configuration of thereference signal in a seventh embodiment of the present invention.

FIG. 15B is a drawing showing another example of the configuration ofthe reference signal in the seventh embodiment of the present invention.

FIG. 16 is a drawing showing an example of the configuration of wirelessframes in the same embodiment.

FIG. 17 is a drawing showing the configuration of a communication systemthat performs MIMO communication.

FIG. 18 is a drawing showing the configuration of the reference signalin a communication system that performs MIMO communication.

FIG. 19 is a drawing showing the configuration of a communication systemthat performs CoMP communication.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

The first embodiment of the present invention will be described below,with references made to drawings.

FIG. 1 is a schematic drawing showing the configuration of acommunication system according to the first embodiment of the presentinvention. The communication system of FIG. 1 includes base stations(transmitter apparatuses, base station apparatuses, eNodeB, eNB, cells,uplink receiver apparatuses) 101 and 102, which constituted each of thecells, and terminal devices (receiver apparatuses, UEs, uplinktransmitter apparatuses) 103 and 104. The base station 101 and theterminal device 103 perform MIMO communication, which is non-CoMP (orSISO (single-input, single-output) communication and transmissiondiversity (TxD)).

The base station 101 and the base station 102 perform communication withthe terminal device 104 by CoMP communication (cooperativecommunication). That is, at least both MIMO communication and CoMPcommunication are performed by the base station 101. Stated differently,the base station 101 houses both a terminal device (first receiverapparatus) 103 that performs MIMO communication and a terminal device(second receiver apparatus) 104 that performs CoMP communication.Although in this case the description is presented for the case in whichthe base station 101 houses the terminal device 103 and the terminaldevice 104 at the same time, this is not a restriction. The base station101 may house the terminal device 103 and the terminal device 104 atdifferent times. The base station 201 is a base station that has thepossibility of cooperating with the base station 101 with respect to theterminal device 104.

The terminal device 103 that performs MIMO communication measures thereference signal transmitted from the base station 101, generatesfeedback information, and reports the generated feedback information tothe base station 101. The terminal device 104 that performs CoMPcommunication measures the reference signal transmitted from the basestation 101 and the reference signal transmitted from the base station102, generates feedback information, and reports the generated feedbackinformation to the base station 101 and/or the base station 102.

FIG. 2 is a drawing showing the condition before the terminal device 104shown in FIG. 1 performs CoMP. The terminal device 104 is housed in thebase station 101. The base stations that have a possibility ofcooperating with the base station 101 with respect to the terminaldevice 104 are both base station 101 and the base station 201. The basestation 101 instructs the terminal device 104 to measure the referencesignal transmitted from the base station 102 and the reference signaltransmitted from the base station 201. The terminal device 104 reports apart or all of the measurement results to the base station 101. Based onthe reported information, the base station 101 determines the basestation to perform CoMP communication. In the case in which the basestation 102 is selected, transition is made to CoMP such as shown inFIG. 1.

FIG. 3A to FIG. 3C are drawings showing examples of the configuration ofthe reference signals (propagation channel status measurement referencesignals) referenced by a terminal device that does not perform CoMP. Theresource block 301 shown in FIG. 3A is transmitted from the base station101 that covers the cell #1, and includes the reference signal. Theresource block 302 shown in FIG. 3B is transmitted from the base station102 that covers the cell #2, and includes the reference signal. Theresource block 303 shown in FIG. 3C is transmitted from the base station103 that covers the cell #3, and includes the reference signal.

Although in this case, the group of 14 resource elements in the timedirection and 12 resource elements in the frequency direction arereferred to as a resource block, this is not a restriction. For example,the group of 14 resource elements in the time direction and 12 resourceelements in the frequency direction may be called a resource block, andthe above-noted resource block may be called a group of resource blocks.The resource elements 301-1 to 301-4 within the resource block 301indicate resource elements onto which the LTE-A reference signal ismapped. The other resource element 301-5, is a resource element ontowhich signals other than an LTE-A reference signal (data signals,control signals, LTE reference signals, reference signals formodulation, or the like) are mapped.

The resource elements 301-1 to 301-4 are resource elements, onto each ofwhich a reference signal corresponding to ports 1 to 4, respectively,which are mutually different ports (logical ports, antenna ports) aremapped. This applies also to the resource elements 302-1 to 302-5 withinthe resource block 302, and the resource elements 303-1 to 303-5 withinthe resource block 303. In this case, although the case in which thereference signals regarding the four ports are placed in one resourceblock is described, the reference signals regarding an arbitrary numberof ports (for example, 1, 2, 4, or 8 ports) may be placed.

An example of the method of measuring the reception quality performed bythe terminal device 103 shown in FIG. 2 will now be described. Theterminal device 103 that is housed in the base station 101 that coversthe cell #1 synthesizes the received signal at the resource elements301-1 to 301-4 onto which the reference signals transmitted from thebase station 101 are mapped for each port. By doing this, the terminaldevice 103 generates replicas of the received signals from the basestation 101. Next, the terminal device 103 performs subtraction of thereplicas from the received signals at the resource elements 301-1 to301-4 and averaging. By doing this, the terminal device 103 calculatesthe signal (interference signal) and the electrical noise powertransmitted from base stations other than the base station 101.

In this case, the cell #2 and the cell #3 transmit signals with the sametime and frequency resources as the resource elements 301-1 to 301-4(that is, puncturing is not done). For this reason, the interferencesignal includes the signal in the cell #2 (the signal mapped onto partof 302-5 in FIG. 3B) and the signal in the cell #3 (the signal mappedonto part of 303-5 in FIG. 3C). The terminal device 103 divides thereplica electrical power by the interference signal and electrical noisepower, so as to calculate the signal-to-interference-and-noise ratio(SINR). The terminal device 103 selects a CQI (Channel QualityIndicator) and an RI (Rank Indicator) so that a prescribed quality atthe calculated SINR is satisfied. The terminal device 103 also selects aPMI (Precoding Matrix Index) so that the calculated SINR increased. Inthis manner, by measuring the resource elements 301-1 to 301-4 in thecell #1, which is a cell housed by the terminal device 103, the terminaldevice 103 generates feedback information that takes into considerationthe interference signals and noise.

FIG. 4A to FIG. 4C are drawings showing examples of the configuration ofreference signals referenced by a terminal device performing CoMP. Theresource block 401 shown in FIG. 4A is transmitted from the base station101 that covers the cell #1, and includes the reference signal. Theresource block 402 shown in FIG. 4B is transmitted from the base station102 that covers the cell #2, and includes the reference signal. Theresource block 403 shown in FIG. 4C is transmitted from the base station201 that covers the cell #3, and includes the reference signal.

The resource elements 401-1 to 401-4 within the resource block 401 areresource elements onto which LTE-A reference signals are mapped. Theresource element 401-6 indicates that signal puncturing is done (thatis, that the signal is not mapped or not transmitted). The otherresource element 401-5 is a resource element onto which signals otherthan an LTE-A reference signal (a data signal, a control signal, an LTEreference signal, a reference signal for modulation, or the like) aremapped. The resource elements 401-1 to 401-4 indicate resource elements,onto each of which a reference signal corresponding to ports 1 to 4,respectively, which are mutually different ports (logical ports, antennaports) are mapped.

Although in this case the description is for the case in which same portas for MIMO is used is CoMP as well, this is not a restriction. Forexample, the resource elements 401-1 to 401-4 may use ports 11 to 14,which are different than ports 1 to 4. This applies also to the resourceelements 302-1 to 302-5 within the resource block 302, and the resourceelements 303-1 to 303-5 within the resource block 303. In this case,however, similar to MIMO communication, although the description is forthe case in which the reference signals for four ports are placed in oneresource block, reference signals of a different number of ports may beplaced.

Next, an example of the method of measuring the reception qualityperformed by the terminal device 104 will be described. The terminaldevice 104 that performs CoMP with the base station 101 that covers thecell #1 and the base station 102 that covers the cell #2 synthesizes thereceived signal at the resource elements 401-1 to 401-4 onto which thereference signals transmitted from the base station 101 are mapped foreach port. By doing this, the terminal device 104 generates replicas ofthe received signals from base station 101. The terminal device 104 alsosynthesizes the received signal at the resource elements 402-1 to 402-4onto which the reference signals transmitted from the base station 102are mapped for each port. By doing this, the terminal device 104generates replicas of the received signals from the base station 102.

In this case, the cell #2 and the cell #3 puncture signals with the sametime and frequency resource with the resource elements 401-1 to 401-4.For this reason, it is possible to measure the replica of the receivedsignal from the base station 101 with good accuracy, and withoutinterference from the signal in the cell #2 and the signal in the cell#3. The same effect is achieved when generating a replica of thereceived signal from the base station 102. The feedback information(CSI: Channel State Information), the information that indicates thechannel matrix or information for a processed channel matrix, or theCQI/PMI/RI is generated from the replicas obtained by the signalreceived from the base station 101 and by the signal received from thebase station 102. In this manner, the terminal device 104 measures theresource elements 401-1 to 401-4 and the resource elements 402-1 to402-4 in the cell #1 and the cell #2, which are cells that perform CoMPwith the terminal device 104. By doing this, the terminal device 104 cangenerate feedback information with good accuracy (with little influencefrom interference).

FIG. 5 is a drawing showing an example of the configuration of wirelessframes transmitted from the base station 101, the base station 102, andthe base station 201. In FIG. 5, the horizontal axis indicates time. Thewireless frame 501 shown as the signal 1 in FIG. 5 is a wireless framethat is transmitted from the base station 101, which covers the cell #1.The wireless frame 502 shown as signal 2 in FIG. 5 is a wireless framethat is transmitted from the base station 102, which covers the cell #2.The wireless frame 503 shown as signal 1 in FIG. 5 is a wireless frametransmitted from the base station 201, which covers the cell #3. Each ofthe wireless frames 501 to 503 includes, respectively, the 10 subframesSF#0 to SF#9. This drawing shows the case in which wireless frames aresynchronized between cells.

The subframes 501-2, 502-2, and 503-2 are subframes in which referencesignals for MIMO communication in the cell #1, the cell #2, and the cell#3 are placed. The subframes 501-3, 502-3, and 503-3 are subframes inwhich reference signals for CoMP communication in the cell #1, the cell#2, and the cell #3 are placed. The other subframes 501-1, 502-1, and503-1 are normal subframes.

In this case, the subframes 501-2, 502-2, and 503-2 are placed in thesame time, and the subframes 501-3, 502-3, and 503-3 are placed in thesame time. The subframes in which a reference signal for MIMOcommunication is placed and the subframes in which a reference signalfor CoMP communication is placed are made to be different subframes.

Between cells capable of CoMP, the subframes in which a reference signalfor CoMP is placed are synchronized (that is, are placed at the sametime). By doing this, the proportion of normal subframes can be madelarge, and the efficiency of locating the reference signals can beimproved.

The subframes in which a reference signal for MIMO communication isplaced and the subframes in which a reference signal for CoMPcommunication is placed are made to be different subframes. By doingthis, in a terminal device that performs MIMO communication, it ispossible to generate feedback information that takes interferencesignals and noise into consideration. Also, in a terminal deviceperforming CoMP communication, it is possible to generate feedbackinformation with good accuracy (with little influence frominterference).

As shown in FIG. 5, in the group of cells in which there is apossibility of performing CoMP, the numbers of subframes in which a CoMPreference signal is placed are set in the same manner. By doing this,there is no need to make new notification of the subframe numbers asinformation indicating the positions of CoMP reference signals in othercells, thereby improving the signaling efficiency.

FIG. 6 is a sequence diagram showing an example of the processingbetween the base station 101 (transmitter apparatus, housing basestation, Serving Cell) and the terminal device 104 according to thepresent embodiment.

First, the base station 101 and the terminal device 104 performcommunication in a mode that is neither the initial mode (TxD mode orthe like) or the MIMO mode (step S601).

In the case of a transition to the MIMO mode, the base station 101 givesthe instruction of feedback for MIMO to the terminal device 104, andmakes notification of the positions of the reference signals for MIMO(step S602). For example, the base station 101 performs signaling thatuses the physical control channel (PDCCH; Physical Downlink ControlChannel) or higher-layer signaling (RRC signaling). In doing this, asthe instruction of MIMO feed back, the feedback method may be specifiedregardless either explicit or implicit, the MIMO mode itself may also bespecified, and both the MIMO mode itself and the feedback method may bespecified.

By making a setting so that the notification of the positions of theMIMO reference signals is the trigger for the MIMO feedback, thenotification itself of the positions of the MIMO reference signals canbe the instruction of the MIMO feedback. The MIMO reference signalpositions may be notified by the numbers of the subframes in which theMIMO reference signals have been placed, or being obtainable assubframes numbers in which placement was made, from a prescribed indexof which notification is made and from another parameter (for example, aunique physical cell number, cell ID or the like) at the terminal deviceside. Additionally, it is possible to give notification of not only thesubframe number, but also information regarding the positions of theresource elements (OFDM symbol number, resource block number, subcarriernumber, frequency offset value, or a index that is specified using alookup table of combination of these).

The terminal device 104 measures the quality of the MIMO referencesignal step S603). Then, the terminal device 104, based on themeasurement results from step S603, generates feedback information forMIMO (step S604). The terminal device 104 then reports the MIMO feedbackinformation generated at step S604 to the base station 101 (step S605).The base station 101 determines the MIMO transmission parameters,referring to the feedback information, and performs MIMO transmissionwith respect to the terminal device 104 (step S606). During the MIMOcommunication, the processing of step S603 to step S606 is repeatedlyperformed.

In the case of transitioning from the MIMO mode to the CoMP mode, thebase station 101 instructs the CoMP feedback to the terminal device 104.The base station 101 notifies the terminal device 104 of the positionsof the CoMP reference signals (step S607). For example, the base station101 performs signaling that uses the physical control channel (PDCCH) orhigher-layer signaling (RRC signaling). In this case, the feedbackmethod may be specified regardless of implicit/explicit as the CoMPfeedback instruction, or the CoMP mode itself may be specified. Bymaking the setting such that the notification of the CoMP referencesignal positions is the trigger for the CoMP feedback, the notificationitself of the CoMP reference signal positions can be the CoMP feedbackinstruction.

The numbers of the subframes in which the CoMP reference signals areplaced in the local cell and in another cell that has the possibility ofperforming CoMP may be notified as the CoMP reference signal positions,and the numbers of subframes into which placement was done may beobtained from a prescribed index of which notification is made and fromanother parameter (for example, a unique physical cell number, cell IDor the like) at the terminal device 104 side. Also, the CoMP referencesignal position in another cell may be information (subframe number orthe like) that specifies a subframe at the local cell that correspondsto a subframe in which the CoMP reference signal is placed in the othercell. By doing this, not only is it possible for the terminal device 104to know the subframe number of the local cell, but also the amount ofprocessing done by the terminal device 104 can be reduced. For example,as the information to notify the terminal device 104 of the subframe inwhich the CoMP reference signal is placed in another cell, notificationcan be given of the subframe number of the corresponding local cell, andnotification may be given of the relative offset value of the subframenumber between the local cell and another cell, or the subframe numberin another cell.

Additionally, notification may be made not only of the subframe number,but also of information regarding the position of a resource element(OFDM symbol number, resource block number, subcarrier number, frequencyoffset value (in the case in which the reference signal is offset infrequency based on the cell ID, the notification of the cell ID ofanother cell notifies implicitly of the reference signal position), oran index that specifies a combination of these, using a lookup table).By doing this, reference signal placement is possible with a high degreeof freedom and, as a result, it is possible to improve the communicationefficiency.

Alternatively, it is possible to adopt a scheme in which the subframenumbers for placement of the CoMP reference signals and the MIMOreference signals are made common for all cells beforehand, wherein whentransitioning to the CoMP mode, notification is made of the relativeoffset value between the subframe numbers of the local cell and anothercell. By doing this, it is possible to improve the efficiency ofsignaling regarding another cell.

It is not absolutely necessary that there be a relationship between theCoMP feedback instruction and the specification of the CoMP referencesignal positions by another cell. For example, the cells (local cell andanother cell) for which specification is made of the CoMP referencesignal positions may be a set of cells for which the reference signal ismeasured, and a set of cells for generating feedback information may bea subset of the set of cells for measurement of the reference signals.

The terminal device 104 measures the quality of the CoMP referencesignal at the local cell and/or another cell (step S608). The terminaldevice 104, based on the results of the measurement in step S608,generates CoMP feedback information (step S609), and reports the CoMPfeedback information generated at step S609 to the base station 101(step S610). The base station 101 determines the CoMP transmissionparameters, referencing the feedback information, cooperates withanother base station and performs CoMP transmission with respect to theterminal device 104 (step S611). During the CoMP communication, theprocessing of step S608 to step S611 is repeatedly performed. Asnecessary, the CoMP reference signal positions (the CoMP referencesignal positions in another cell having the possibility of performingCoMP) may be notified to the terminal device 104 from the base station101.

When switching to the transmitting mode, by instruction of the feedbackmethod and notification of the positions of the reference signals, it ispossible to perform efficient signaling regarding the feedback. Byassociating the instruction of the feedback method with the notificationof the reference signal positions, it is possible to reduce thesignaling overhead.

FIG. 7 is a simplified block diagram showing an example of theconfiguration of the base station (transmitter apparatus) 101 in thepresent embodiment. Because the configurations of the base station 102and the base station 201 are the same as that of the base station 101,the description thereof will be omitted herein.

The base station 101 includes coding units 701-1 and 701-2, scramblingunits 702-1 and 702-2, modulating units 703-1 and 703-2, a layer mappingunit 704, a precoding unit 705, a reference signal generating unit 706,resource element mapping units 707-1 and 707-2, OFDM signal generatingunits 708-1 and 708-2, transmitting antennas 709-1 and 709-2, areceiving antenna 710, a received signal processing unit 711, a feedbackinformation processing unit 712, and a higher-layer 713.

The higher layer 713 outputs the transmitted data (bit stream) for thenumber of code words for each code word to the coding units 701-1 and701-2. The coding units 701-1 and 701-2, based on the coding rate outputby the feedback information processing unit 712, performs errorcorrection coding and rate mapping processing with respect to the signaloutput by the higher layer 713, and outputs the result to the scramblingunits 702-1 and 702-2. The scrambling units 702-1 and 702-2 multiply thesignal output by the coding units 701-1 and 701-2 by a scrambling code,and output the result to the modulating units 703-1 and 703-2. Themodulating units 703-1 and 703-2, based on the modulation method outputby the feedback information processing unit 712, performs modulationprocessing of the signal output by the scrambling units 702-1 and 702-2for PSK (phase-shift keying) modulation or QAM (quadrature amplitudemodulation) or the like and outputs the result to the layer mapping unit704.

The layer mapping unit 704, based on the mapping scheme output by thefeedback information processing unit 712, distributes the modulationsymbol stream output from the modulating units 703-1 and 703-2 to eachlayer, and outputs the signals for the number of layers to the precodingunit 705. The precoding unit 705, based on the precoding matrix outputby the feedback information processing unit 712, performs precodingprocessing of the modulation symbol stream for each layer output by thelayer mapping unit 704, and outputs the result to the resource elementmapping units 707-1 and 707-2. More specifically, the precoding unit 705multiplies the modulation symbol stream for each layer output by thelayer mapping unit 704 by the precoding matrix.

The reference signal generating unit 706 generates a reference signalfor MIMO and for CoMP, and outputs the result to the resource elementmapping units 707-1 and 707-2. In this case, because the referencesignal generating unit 706 uses the same stream to generate the MIMOreference signals and the CoMP reference signals, it is possible toreduce the size of the circuitry and the amount of processing requiredto generate the reference signals. For example, the reference signalgenerating unit 706 can use a stream generated in accordance with thecell ID for both the MIMO reference signals and the CoMP referencesignals. Alternatively, the reference signal generating unit 706 mayperform generation so that the streams used in generating the MIMOreference signals and the CoMP reference signals differ. By performinggeneration so that the streams used in generating the MIMO referencesignals and the CoMP reference signals differ, it is possible to reducethe interference, even in the case in which both the MIMO referencesignals and the CoMP reference signals between different cells aretransmitted using the same resource.

The resource element mapping units 707-1 and 707-2, based on themodulation symbol mapping scheme output by the feedback informationprocessing unit 712, map the modulation symbol stream precoded in theprecoding unit 705 and the reference signal generated by the referencesignal generating unit 706 onto the prescribed resource elements, andoutput signals for the number of transmitting antennas to the OFDMsignal generating units 708-1 and 708-2. In this case, the positions ofresource elements onto which CoMP reference signals are mapped in eachcell performing CoMP are shared beforehand between cells (between basestations). The resource element mapping units 707-1 and 707-2 do not mapmodulation symbols onto resource elements of the local cell thatcorrespond to the resource element onto which the CoMP reference signalsare mapped in the cells performing CoMP.

The OFDM signal generating units 708-1 and 708-2 convert the group ofresource blocks output from the resource element mapping units 707-1 and707-2 to OFDM signals and output the results to the transmittingantennas 709-1 and 709-2. The transmitting antennas 709-1 and 709-2transmit the signals output by the OFDM signal generating units 708-1and 708-2 as downlink transmitted signals to the terminal device 104 orthe like, from the transmitting antennas 709-1 and 709-2.

The receiving antenna 710 receives the uplink received signal from theterminal device 104 or the like and outputs it to the received signalprocessing unit 711. The received signal processing unit 711, afterperforming prescribed processing of the signal output from the receivingantenna 710, outputs the result to the feedback information processingunit 712 as feedback information. The feedback information processingunit 712, using the feedback information reported from the terminaldevice performing MIMO communication, changes items such as the codingrate in the coding units 701-1 and 701-2, the modulation method in themodulating units 703-1 and 703-2, the mapping scheme in the layermapping unit 704, the precoding matrix in the precoding unit 705, andthe modulation symbol mapping scheme in the resource element mappingunits 707-1 and 707-2 and outputs the result to various units.

The feedback information processing unit 712, rather than just using thefeedback information reported from a terminal device performing CoMPcommunication to change the items such as the coding rate in the codingunits 701-1 and 701-2, the modulation method in the modulating units703-1 and 703-2, the mapping scheme in the layer mapping unit 704, theprecoding matrix in the precoding unit 705, and the modulation symbolmapping scheme in the resource element mapping units, also generates andsends to various units information shared between cells for performingCoMP (such as scheduling information and precoding information) based onthe feedback information.

FIG. 8 is a simplified block diagram showing an example of theconfiguration of a terminal device 104 (receiver apparatus) in thepresent embodiment. Because the configuration of the terminal device 103is the same as that of the terminal device 104, its description will beomitted herein.

The terminal device 104 has receiving antennas 801-1 and 801-2, OFDMsignal demodulating units 802-1 and 802-2, resource element demappingunits 803-1 and 803-2, a filter unit 804, a precoding unit 805, a layerdemapping unit 806, demodulating units 807-1 and 807-2, descramblingunits 808-1 and 808-2, decoding units 809-1 and 809-2, a higher layer810, a reference signal measuring unit 811, a feedback informationgenerating unit 812, a transmitted signal generating unit 813, and atransmitting antenna 814.

The receiving antennas 801-1 and 801-2 receive the downlink receivedsignals transmitted by the base station 101 or the like and output thesignals from the number of receiving antennas to the OFDM signaldemodulating units 802-1 and 802-2. The OFDM signal demodulating units802-1 and 802-2 perform OFDM demodulation processing of the signalsoutput by the receiving antennas 801-1 and 801-2, and output signals fora resource block group to the resource element demapping units 803-1 and803-2.

The resource element demapping units 803-1 and 803-2 obtain thereference signals from the resource elements at the positions notifiedfrom the base station in step S602 and step S607 in FIG. 6, and outputthem to the reference signal measurement unit 811. The resource elementdemapping units 803-1 and 803-2 output the received signals fromresource elements onto which reference signals are not mapped to thefilter unit 804. In the case in which the terminal device 104 performsCoMP, the terminal device 104 is notified in step S607 in FIG. 6 fromthe base station 101 of the position of a resource element onto which aCoMP reference signal is mapped in another cooperating cell.

In the resource element of the local cell that corresponds to thisresource element, modulating symbol puncturing is performed in theresource element mapping units 707-1 and 707-2. For this reason, theresource element demapping units 803-1 and 803-2 may make output to thefilter unit 804 after destruction and/or depuncturing of the receivedsignal. By doing this, it is possible to reduce interference and noise,and possible to improve the quality of received data.

The filter unit 804 performs filtering processing with respect to thereceived signals output from the resource element demapping units 803-1and 803-2, and outputs the results to the deprecoding unit 805. Thedeprecoding unit 805 performs deprecoding processing with respect to thesignal that was filtered by the filter unit 804, this corresponding tothe precoding done by the precoding unit 705, and outputs signals forthe number of layers to the layer demapping unit 806. The layerdemapping unit 806 performs joining processing with respect to thesignal output by the deprecoding unit 805, this corresponding to thelayer mapping unit 704, converts the signals for each layer to signalsfor each code word, and outputs the result to the demodulating units807-1 and 807-2.

The demodulating units 807-1 and 807-2 perform demodulation processingwith respect to the signals for each code word converted by the layerdemapping unit 806, this corresponding to the modulation processing inthe modulating units 703-1 and 703-2, and output the results to thedescrambling units 808-1 and 808-2. The descrambling units 808-1 and808-2 multiply the signals output by the demodulating units 807-1 and807-2 by the conjugate code of the scrambling code used in thescrambling units 702-1 and 702-2 (divided by the scrambling code), andoutput the results to the decoding units 809-1 and 809-2. The decodingunits 809-1 and 809-2 perform rate demapping processing and errorcorrection decoding processing with respect to the signals output by thedescrambling units 808-1 and 808-2, obtain received data for each codeword, and output signals for the number of code words to the higherlayer 810.

In this case, in the filtering processing performed by the filter unit804, the transmitted signals of each of the transmitting antennas 709-1and 709-2 in FIG. 7 are detected from the received signals for each ofthe receiving antennas 801-1 and 801-2, using a method such as ZF (zeroforcing), MMSE (minimum mean square error), or MLD (maximum likelihooddetection). It is possible, by referencing a known signal precoded inthe same manner as data, perform processing at the filter unit 804 andprocessing at the deprecoding unit 805 simultaneously when detecting thetransmitted signals of each layer.

The reference signal measuring unit 811 measures the reference signalsacquired by the resource element demapping units 803-1 and 803-2, andoutputs the measurement results to the feedback information generatingunit 812. In the case in which the terminal device 104 is performingMIMO communication, the feedback information generating unit 812generates the above-described MIMO feedback information, and outputs itto the transmitted signal generating unit 813. In the case in which theterminal device 104 is performing CoMP communication, the feedbackinformation generating unit 812 generates the above-described CoMPfeedback information and outputs it to the transmitted signal generatingunit 813.

The transmitted signal generating unit 813 converts the feedbackinformation generated by the feedback information generating unit 812 toa transmitted signal, and outputs the result to the transmitting antenna814. The transmitting antenna 814 transmits the signal output by thetransmitted signal generating unit 813 to the base station 101 as theuplink transmitted signal.

In this manner, for the first reference signal that is referenced by aterminal device that does not perform CoMP, puncturing is not done bythe base station. In contrast, the base station does do puncturing inthe case of a second reference signal that is referenced by a terminaldevice performing CoMP, and places the first and second referencesignals in different subframes. By doing this, the terminal device cangenerate the feedback information with high accuracy. When transitioningto the MIMO mode, notification is made by the base station to theterminal device of the positions of the first reference signals. Whentransitioning to the CoMP mode, notification is made by the base stationto the terminal device of the position of the second reference signal.By doing this, efficient placement of reference signals and signalingare possible for feedback.

The resource element mapping unit 707-1 of the base station 101, whichis a transmitter apparatus, functions as the first mapping unit 707-1-1and the second mapping unit 707-1-2. The resource element mapping unit707-2, similarly, functions as the resource element mapping unit 707-1.

The transmitting antenna 709-1 of the base station 101 functions as thereference signal transmitting unit 709-1-1 and the notifying unit709-1-2. The transmitting antenna 709-2, similarly, functions as thetransmitting antenna 709-1.

In the base station 101, the reference signal transmitting unit 709-1-1transmits both the first reference signal and a second reference signal,that is different from the first reference signal, to both the firstreceiver apparatus that performs non-cooperative communication (forexample, the terminal device 104) and a second receiver apparatus thatperforms cooperative communication (for example, the terminal device103), respectively.

In the base station 101, the notifying unit 709-1-2 instructs the firstreceiver apparatus to measure the first reference signal, and instructsthe second receiver apparatus to measure the second reference signal.

In the base station 101, the first mapping unit 707-1-1 may map thefirst reference signal and the second reference signal onto differentresources.

In the base station 101, the first mapping unit 707-1-1 may use the samestream as both the first reference signal and the second referencesignal.

In the base station 101, the second mapping unit 707-1-2 may place thefirst reference signal and the second reference signal in differentsubframes.

In the base station 101, the reference signal transmitting unit 709-1-1may transmit both the first reference signal and the second referencesignal that differs from the first reference signal to a first receiverapparatus (for example, the terminal device 104) that performsnon-cooperative communication and a second receiver apparatus (forexample, the terminal device 103) that performs cooperativecommunication.

The notifying unit 709-1-2 may notify the first receiver apparatus ofinformation that specifies the position of the first reference signal,and notify the second receiver apparatus of information that specifiesthe position of the second reference signal.

The reference signal measuring unit 811 of the terminal device 104,which is a receiver apparatus, functions as a first reference signalmeasuring unit 811-1 and a second reference signal measuring unit 811-2.

The feedback information generating unit 812 of the terminal device 104functions as the first feedback information generating unit 812-1 andthe second feedback information generating unit 812-2.

In the terminal device 104, the first reference signal measuring unit811-1 measures the first reference signal that differs from the firstreference signal, based on the instruction to measure the firstreference signal from the transmitter apparatus that switches betweennon-cooperative communication and cooperative communication.

In the terminal device 104, the second reference signal measuring unit811-2 measures the second reference signal, based on the instruction tomeasure the second reference signal from the transmitter apparatus.

In the terminal device 104, the first feedback information generatingunit 812-1 may use the first reference signal measurement results togenerate first feedback information, and the second feedback informationgenerating unit 812-2 using the second reference signal measurementresults to generate second feedback information that differs from thefirst feedback information.

Second Embodiment

In the first embodiment, the description is for the case in which thesubframes in which CoMP reference signals are placed are synchronized(placed at the same time) between cells capable of CoMP. In the secondembodiment of the present invention, the case in which the CoMPreference signals are placed in different subframes between cellscapable of CoMP will be described.

Because the base station and terminal device configurations in thesecond embodiment are the same as those of the base station (FIG. 7) andthe terminal device (FIG. 8) in the first embodiment, their descriptionswill be omitted herein.

The present embodiment will be described below, with references made tothe drawings.

FIG. 9A to FIG. 9C are drawings showing examples of the configuration ofthe reference signal that are referenced by the terminal device thatperforms CoMP. In FIG. 9A to FIG. 9C, the horizontal axis representstime and the vertical axis represents frequency. In the presentembodiment, the description is for a cell configuration that is similarto that shown in FIG. 1 and FIG. 2.

The resource block 901 shown in FIG. 9A is transmitted from the basestation 101 that covers the cell #1, and at the cell #1 there istransmission from each cell at the same time as a resource block thatincludes a CoMP reference signal. The resource block 902 shown in FIG.9B is transmitted from the base station 102 that covers the cell #2,this being a resource block that is transmitted from each cell at thesame time as the resource block that includes the CoMP reference signalat the cell #1. The resource block 903 shown in FIG. 9C is transmittedfrom the base station 201 that covers the cell #3, being a resourceblock that is transmitted from each cell at the same time as theresource block that includes the CoMP reference signal at the cell #1.

The resource elements 901-1 to 901-4 within the resource block 901 areresource elements onto which LTE-A reference signals are mapped. Theother resource element 901-5 is a resource element onto which a signalother than an LTE-A reference signal (that is, a data signal, a controlsignal, an LTE control signal, a reference signal for modulation, or thelike) is mapped. The resource element 902-2 is a resource element at thecell #2 having the same frequency and the same time as the resourceelement with which the CoMP reference signal is transmitted from thecell #1, in which the modulation symbols are punctured. What is shown isthe case in which transmission is made at the same frequency and time asthe resource block 902 and also in which the CoMP reference signal isplaced only at the cell #1. If a CoMP reference signal is placed atanother cell, puncturing is done even at the resource element at thecell #2 at the same frequency and same time as the resource element ontowhich the reference signal of that cell is mapped. The same applies tothe resource elements 903-1 and 903-2 within the resource block 903 atthe cell #3 as with respect to the cell #2.

An example of the method of measuring the quality of receiving by theterminal device 104 in FIG. 1 will now be described. The terminal device104, which performs CoMP with the base station 101 that covers the cell#1 and the base station 102 that covers the cell #2 synthesizes thereceived signal at the resource elements 901-1 to 901-4 onto which thereference signals transmitted from the base station 101 are mapped foreach port. By doing this, the terminal device 104 generates replicas ofthe received signals from the base station 101. In this case, the cell#2 and the cell #3 do signal puncturing at the same time and samefrequency resources as the resource elements 901-1 to 901-4 (forexample, the resource elements 902-2 and 903-2).

For this reason, the replicas of received signals from the base station101 are not interfered with by the signal at the cell #2 and the signalat the cell #3, it is possible to measure with accuracy. From theobtained replicas of received signals from the base station 101, theterminal device 104 generates feedback information (CSI (channel stateinformation)), information that indicates a channel matrix, orinformation for a processed channel matrix. In this manner, the terminaldevice 104 measures the resource elements 901-1 to 901-4 at the cell #1,which is a cell that performs CoMP with the terminal device 104, so thatit is possible to generate the feedback information with good accuracy(with little influence from interference).

FIG. 10 is a drawing showing an example of the configuration of wirelessframes transmitted from the base station 101, the base station 102, andthe base station 201. In FIG. 10, the horizontal axis indicates time.The wireless frame 1001 shown as signal 1 in FIG. 10 is transmitted fromthe base station 101 that covers the cell #1. The wireless frame 1002shown as signal 2 in FIG. 10 is transmitted from the base station 102that covers the cell #2. The wireless frame 1003 shown as signal 3 inFIG. 10 is transmitted from the base station 201 that covers the cell#3. Each of the wireless frames 1001, 1002, and 1003 includes,respectively, the 10 subframes SF#0 to SF#9. This drawing shows the casein which wireless frames are synchronized between cells.

The subframes 1001-2, 1002-2, and 1003-2 are subframes in which MIMOreference signals for MIMO communication in the cell #1, the cell #2 andthe cell #3 are placed. The subframes 1001-2, 1002-2, and 1003-2 can besubframes in which MIMO reference signals are placed, similar to FIG. 3Ato FIG. 3C. The subframes 1001-3, 1002-3, and 1003-3 are subframes inwhich CoMP reference signals in the cell #1, the cell #2, and the cell#3 are placed.

The subframes 1001-4, 1002-4, and 1003-4 are each subframes in whichpuncturing is done in the resource elements onto which CoMP referencesignals in any of the cell #1, the cell #2, and the cell #3 are mapped.For example, in the subframe SF#6, it is possible to use the referencesignals placement shown in FIG. 9A to FIG. 9C. The other subframes,1001-1, 1002-1 and 1003-1 are normal subframes (subframes in which areference signal is not placed or subframes that do not performpuncturing).

As described above, the terminal device 104 in FIG. 1 can measure theCoMP reference signal at the cell #1 in subframe SF#6 with highaccuracy. In the same manner, the terminal device 104 can measure theCoMP reference signals at the cell #2 in the subframe SF#7 with highaccuracy. In this manner, the terminal device 104 can generate eachfeedback information with good accuracy (with little influence frominterference), and report these separately to the base stations. Bydoing this, because the feedback information is temporally dispersed, itis possible to improve the feedback efficiency.

Alternatively, the terminal device 104 can store each of the accuratemeasurement results (with little influence from interference) andgenerate feedback information from the measurement results of aplurality of cells (for example, the cell #1 and the cell #2), andreport the result to the base station. In this case, the terminal device104 can not only generate, as the feedback information, CSI (informationindicating the channel matrix or the processed channel matrix), but alsocan generate CQI/PMI/RI, thereby enabling generating of high-accuracyfeedback information that takes the performance of the terminal deviceinto consideration.

In this manner, the base station does not perform puncturing for thefirst reference signal that is referenced by a terminal device that doesnot perform CoMP. In contrast, the base station performs puncturing forthe second reference signal that is referenced by a terminal device thatperforms CoMP, and places the first reference signal and the secondreference signal into different subframes. By doing this, the terminaldevice can generate highly accurate feedback information.

Third Embodiment

In the first embodiment, the description is for the case in whichnotification is made of the position of the first reference signal whentransitioning to the MIMO mode, and notification is made of the positionof the second reference signal when transitioning to the CoMP mode. Inthe third embodiment, the description will be for the case in which theposition of the first reference signal is notified to the terminaldevice from the base station, and notification is made of the positionof the second reference signal to the terminal device from the basestation when transitioning to the CoMP mode.

Because the configurations of the base station and the terminal devicein the third embodiment are the same as the base station (FIG. 7) andthe terminal device (FIG. 8) in the first embodiment, detaileddescriptions thereof will be omitted herein.

The present embodiment is described below, with references made to FIG.11. FIG. 11 is a sequence diagram showing an example of the processingbetween the base station 101 (transmitter apparatus, housing basestation, Serving Cell) and the terminal device in the presentembodiment.

First, the base station notifies the terminal device of informationindicating the position of the MIMO reference signal. The terminaldevice receives this information (step S1101). The base station and theterminal device communicate in the transmitting mode that is neither theinitial mode (TxD mode or the like) or the MIMO mode (step S1102). Inthis case, the MIMO reference signal positions may be notified by thenumbers of the subframes in which the MIMO reference signals have beenplaced from the base station to the terminal device, or be obtainable assubframes numbers in which placement was made, from a prescribed indexof which notification is made and from another parameter (for example,cell ID or the like) at the terminal device side. Additionally, it ispossible to give notification of not only the subframe numbers, but alsoinformation regarding the position of the resource elements (OFDM symbolnumber, resource block number, subcarrier number, frequency offsetvalue, or a index that is specified using a lookup table of combinationof these) from the base station to the terminal device.

In the case of transition to the MIMO mode, the base station instructsthe terminal device regarding the feedback for MIMO (step S1103). Inthis case, by the MIMO feedback instruction, the feedback method may bespecified regardless of explicit/implicit, or the MIMO mode itself maybe specified.

Upon receiving the MIMO feedback instruction from the base station, theterminal device uses the position information of the MIMO referencesignals of which notification was made to measure the quality of theMIMO reference signals (step S1104). The terminal device, based on themeasurement results at step S1104, generates MIMO feedback information(step S1105). The terminal device reports the MIMO feedback informationgenerated at step S1105 to the base station (step S1106). The basestation determines the MIMO transmission parameters, referring to thefeedback information, and performs MIMO transmission with respect to theterminal device (step S1107). During the MIMO communication, theprocessing of step S1104 to step S1107 is repeatedly performed.

In the case of transitioning from the MIMO mode to the CoMP mode, thebase station instructs the CoMP feedback to the terminal device, andgives notification of the CoMP reference signal position (for example,signaling using the physical control channel (PDCCH) or higher-layersignaling (RRC signaling)) (step S1108). In this case, the feedbackmethod may be specified regardless of implicit/explicit, or the CoMPmode itself may be specified. By making the setting such that thenotification of the CoMP reference signal positions is the trigger forthe CoMP feedback, the notification itself of the CoMP reference signalpositions can be the CoMP feedback instruction.

The numbers of the subframes in which the CoMP reference signals areplaced in the local cell and another cell that has the possibility ofperforming CoMP may be notified as the CoMP reference signal positions,or being obtainable as subframe numbers in which placement was made,from a prescribed index of which notification is made and from anotherparameter (for example, cell ID or the like) at the terminal deviceside. Additionally, it is possible for base station to notify theterminal device of not only the subframe numbers, but also informationregarding the resource element positions (the OFDM symbol number,resource block number, subcarrier number, frequency offset value, or anindex that is specified by a lookup table of a combination thereof).

The CoMP feedback instruction and the other cell that specify the CoMPreference signal positions are not necessarily associated with oneanother. For example, cells specifying the CoMP reference signalpositions (local cells or other cells) may be a set of cells formeasurement of the reference signals, a set of cells for generation offeedback information may be a subset of the set of cells for measurementof the reference signals.

The terminal device measures the quality of the CoMP reference signalsof the local cells and/or other cells (step S1109). The terminal device,based on the measurement results, generates CoMP feedback information(step S1110). The terminal device reports the generated CoMP feedbackinformation to the base station (step S1111). The base stationdetermines the CoMP transmission parameters, referencing the feedbackinformation, and performs CoMP transmission to a terminal device,cooperating with another base station (step S1112). During the CoMPcommunication, the processing of step S1109 to step S1110 is repeatedlyperformed. As necessary, the CoMP reference signal positions (the CoMPreference signal positions in another cell having the possibility ofperforming CoMP) may be notified to the terminal device from the basestation.

The positions of the reference signals for MIMO, which is a basictransmission mode, are notified by the base station to the terminaldevice beforehand, and when the transmission mode is switched,notification is made of the feedback method instruction. Also, whenswitching to the CoMP mode, notification is made of the CoMP referencesignal positions from the base station to the terminal device. By doingthis, it is possible to improve the efficiency of feedback-relatedsignaling. By associating the feedback method instruction with thereference signal position notification, it is possible to reduce theoverhead in signaling.

By the base station notifying terminal device of the MIMO referencesignal position, it is possible to acquire and use the MIMO referencesignal even at a terminal device which has transitioned to the CoMPmode. For example, a terminal device in the CoMP mode also can measurethe MIMO reference signal and calculate the SINR assuming MIMOtransmission. By further reporting this feedback information based onthis SINR to the base station, it is possible to make a smoothtransition from the CoMP mode to the MIMO mode, or to dynamically switchbetween the CoMP mode and the MIMO mode. The transfer rate based on theSINR calculated by the terminal device can be compared with the transferrate during the CoMP mode, to enable reporting by the terminal device tothe base station as to which of the transmission modes is preferable.Because this enables a smooth transition from the CoMP mode to the MIMOmode or dynamic switching between the CoMP mode and the MIMO mode,efficient use of bandwidth is possible.

Fourth Embodiment

In the first embodiment, the description was for the case in whichnotification is made of the first reference signal position by the basestation to the terminal device at the time of transition to the MIMOmode, and notification is made of the second reference signal positionby the station to the terminal device at the time of transition to theCoMP mode. In the fourth embodiment of the present invention, the casedescribed is that in which the first reference signal position and thesecond reference signal position are notified from the base station tothe terminal device, with MIMO or CoMP feedback instruction being madeat the time of a transition to the MIMO mode or the CoMP mode.

Because the configurations of the base station and the terminal devicein the fourth embodiment are the same as the base station (FIG. 7) andthe terminal device (FIG. 8) in the first embodiment, detaileddescriptions thereof will be omitted herein.

The present embodiment is described below, with references made to FIG.12. FIG. 12 is a sequence diagram showing an example of the processingbetween a base station 101 (transmitter apparatus, housing base station,Serving Cell) and a terminal device in the present embodiment.

First, the base station and the terminal device perform communication ina transmission mode that is neither the initial mode (TxD mode or thelike) or the MIMO mode or CoMP mode (step S1201).

In the case of transition to the MIMO mode, the base station makesnotification to the terminal device of the MIMO reference signal (firstreference signal) positions and the CoMP reference signal (secondreference signal) positions. The base station gives a MIMO feedbackinstruction to the terminal device (step S1202). In this case, althoughthe description is for the case of the notification of the firstreference signal position and the second reference signal position atthe time of transition to the MIMO mode (step S1202), this is not arestriction, and notification prior thereto may be given. For example,it is possible to use a method such as signaling in a random accessprotocol or synchronized handover.

The terminal device that has received the MIMO feedback instruction fromthe base station uses the notified MIMO reference signal positioninformation to measure the quality of the MIMO reference signal (stepS1203). The terminal device, based on the measurement results at stepS1203, generates MIMO feedback information (step S1204). The terminaldevice reports the MIMO feedback information that is generated at stepS1204 to the base station (step S1205). The base station determines theMIMO transmission parameters, referencing the feedback information, andperforms MIMO transmission to the terminal device (step S1206). Duringthe MIMO communication, the processing of step S1203 to step S1206 isrepeatedly performed.

In the case of a transition from the MIMO mode to the CoMP mode, thebase station gives a CoMP feedback instruction to the terminal device(step S1207).

The terminal device measures the quality of the CoMP reference signalsof a local cell and/or another cell (step S1208). The terminal device,based on the measurement results at step S1208, generates CoMP feedbackinformation (step S1209). The terminal device reports the CoMP feedbackinformation generated at step S1209 to the base station (step S1210).The base station determines the CoMP transmission parameters,referencing the feedback information, and perform CoMP transmission tothe terminal device, cooperating with another base station (step S1211).During the CoMP communication, the processing of step S1208 to stepS1211 is repeatedly performed. As necessary, the CoMP reference signalpositions (the CoMP reference signal positions in another cell havingthe possibility of performing CoMP) may be notified to the terminaldevice from the base station.

The positions of the MIMO reference signals and the positions of theCoMP reference signal are notified by the base station to the terminaldevice beforehand, and when the transmission mode is switched,notification is made of the feedback method instruction. By doing this,it is possible to improve the efficiency of feedback-related signaling.

By the base station notifying the terminal device of the MIMO referencesignal positions and the CoMP reference signal positions beforehand, itis possible to acquire and use the MIMO reference signals at even theterminal device that has transitioned to the CoMP mode. For example, aterminal device in the CoMP mode also can measure the MIMO referencesignals and calculate the SINR assuming MIMO transmission. By furtherreporting of this feedback information based on SINR by the terminaldevice to the base station, it is possible to make a smooth transitionfrom the CoMP mode to the MIMO mode, or to switch between the CoMP modeand the MIMO mode dynamically.

The transfer rate based on the SINR calculated by the terminal devicecan be compared with the transfer rate during the CoMP mode, to enablereporting by the terminal device to the base station as to which of thetransmission mode is preferable. Because this enables a smoothtransition from the CoMP mode to the MIMO mode or dynamic switchingbetween the CoMP mode and the MIMO mode, efficient use of bandwidth ispossible. In the reverse case, in the terminal device in whichtransition has been made to the MIMO mode, it is possible to acquire anduse the CoMP reference signals. For example, a terminal device in theMIMO can also measure the CoMP reference signals and calculate the SINRwith high accuracy. Alternatively, because the position of modulationsymbols punctured at the local cell can be known by terminal device, itis possible to perform data demodulation and decoding that takes thisinto consideration.

In this embodiment as well, it is possible to use the same informationas the reference signal position information as in the first to thirdembodiments. With regard to the notification of the reference signalpositions as well, it is possible to use signaling that is the same asin the first to third embodiments. In the present embodiment as well,there is no restriction to an association between the CoMP feedbackinstruction and the other cell that specifies the CoMP reference signalpositions.

Fifth Embodiment

In the first embodiment, the description was for the case in whichnotification is made of the first reference signal position at the timeof transition to the MIMO mode, and notification is made of the secondreference signal position at the time of transition to the CoMP mode. Inthe fifth embodiment of the present invention, the description is forthe case in which the first and second reference signal positions arefirst reported, and then instruction is given for either MIMO or CoMPfeedback when a transition is made to either the MIMO mode or the CoMPmode.

Because the configurations of the base station and the terminal devicein the fifth embodiment are the same as the base station (FIG. 7) andthe terminal device (FIG. 8) in the first embodiment, detaileddescriptions thereof will be omitted herein.

The present embodiment is described below, with references made to FIG.13. FIG. 13 is a sequence diagram showing an example of the processingbetween a base station 101 (transmitter apparatus, housing base station,Serving Cell) and a terminal device in the present embodiment.

The base station makes a notification to the terminal device of thepositions of the MIMO reference signals (first reference signal) and theposition of the CoMP reference signals (second reference signal) (stepS1301).

The base station and the terminal device are communicating in atransmission mode that is neither the initial mode (TxD mode or thelike) or the MIMO or CoMP mode (step S1302).

In the case of transition to the MIMO mode, the base station instructsthe MIMO feedback to the terminal device (step S1303).

The terminal device that has received the MIMO feedback instruction fromthe base station uses the notified MIMO reference signal positioninformation to measure the quality of the MIMO reference signal (stepS1304). The terminal device, based on the measurement results of stepS1304, generates MIMO feedback information (step S1304). The terminaldevice reports the MIMO feedback information generated at step S1304 tothe base station (step 1306). The base station references the feedbackinformation and determines the MIMO transmission parameters, andperforms MIMO transmission to the terminal device (step S1307). Duringthe MIMO communication, the processing of step S1304 to step S1307 isrepeatedly performed.

In the case of transition from the MIMO mode to the CoMP mode, the basestation instructs the CoMP feedback to the terminal device (step S1308).

The terminal device measures the quality of the CoMP reference signalsof the local cell and/or another cell (step S1309). The terminal device,based on the measurement results at step S1309, generates CoMP feedbackinformation (step S1310). The terminal device reports the CoMP feedbackinformation generated at step S1310 to the base station (step S1311).The base station references the feedback information to determine theCoMP transmission parameters and performs CoMP transmission to theterminal device, cooperating with another base station (step S1312).During the CoMP communication, the processing of step S1309 to step 1312is repeatedly performed.

When the MIMO reference signal positions and the CoMP reference signalpositions are notified from the base station to the terminal devicebeforehand and then the transmission mode is switched, notification ismade of a feedback method instruction. By doing this, it is possible toimprove the efficiency of feedback-related signaling.

When the MIMO reference signal position and the CoMP reference signalposition are notified to the terminal device from the base stationbeforehand, even at a terminal device that has transitioned to the CoMPmode, it is possible to acquire and use the MIMO reference signals. Forexample, the CoMP mode terminal device also measures the MIMO referencesignals and can calculate the SINR for the case of assuming MIMOtransmission. By further reporting this feedback information based onSINR, it is possible to make a smooth transition from the CoMP mode tothe MIMO mode, or to dynamically switch between the CoMP mode and theMIMO mode.

The transfer rate based on the SINR calculated by the terminal devicecan be compared with the transfer rate during the CoMP mode, to enablereporting to the base station as to which of the transmission modes ispreferable. By doing this, it is possible to make a smooth transitionfrom the CoMP mode to the MIMO mode or dynamically switch between theCoMP mode and the MIMO mode, thereby enabling efficient usage offrequency spectrum. In the reverse case, a terminal device that hastransitioned to the MIMO mode can also acquire and use the CoMPreference signals. For example, the MIMO mode terminal device also canmeasure the CoMP reference signals and calculate the SINR with highaccuracy. Alternatively, because the position of modulation symbolspunctured at the local cell can be known, it is possible to perform datademodulation and decoding that takes this into consideration.

In this embodiment as well, it is possible to use the same informationas the reference signal position information as in the first to thirdembodiments. In the present embodiment as well, there is no restrictionto an association between the CoMP feedback instruction and the othercell that specifies the CoMP reference signal positions.

Sixth Embodiment

In the third embodiment, the description was for the case of a CoMP modeterminal device reporting CoMP feedback information a base station. Inthe sixth embodiment of the present invention, the description will befor the case in which a CoMP mode terminal device reports MIMO feedbackin addition to CoMP feedback to the base station.

Because the configurations of the base station and the terminal devicein the sixth embodiment are the same as the base station (FIG. 7) andthe terminal device (FIG. 8) in the first embodiment, detaileddescriptions thereof will be omitted herein.

The present embodiment will be described below, with references made toFIG. 14. FIG. 14 is a sequence diagram showing an example of theprocessing between a base station 101 (transmitter apparatus, housingbase station, Serving Cell) and a terminal device in the presentembodiment.

First, the base station notifies the terminal device of informationindicating the MIMO reference signal position. The terminal deviceacquires this information from the base station (step S1401). The basestation and the terminal device are communicating in a transmission modethat is neither the initial mode (TxD mode or the like) nor the MIMOmode (step S1402).

In the case of a transition to the MIMO mode, instruction is made of theMIMO feedback by the base station to the terminal device (step S1403).

The terminal device that has received an instruction of MIMO feedbackfrom the base station uses the notified MIMO reference signal positioninformation and measures the quality of the MIMO reference signal (stepS1404). The terminal device, based on the measurement results at stepS1404, generates MIMO feedback information (step S1405). The terminaldevice reports the MIMO feedback information generated at step S1405 tothe base station (step S1406). The base station references the feedbackinformation and determines the MIMO transmission parameters, andperforms MIMO transmission to the terminal device (step S1407). Duringthe MIMO communication, the processing of step S1404 to step S1407 isrepeatedly performed.

In the case of a transition from the MIMO mode to the CoMP mode, thebase station gives a CoMP feedback instruction to the terminal deviceand notifies it of the CoMP reference signal position (step S1408).

The terminal device measures the quality of the MIMO reference signal atthe local cell (step S1409). The terminal device, based on themeasurement results at step S1409, generates MIMO feedback information(step S1410). The terminal device also measures the quality of the CoMPreference signals at the local cell and/or another cell (step S1411).The terminal device, based on the measurement results at step S1411,generates CoMP feedback information (step S1412). The terminal devicereports the MIMO feedback information generated at step S1412 and theCoMP feedback information to the base station (step S1413). The basestation references the feedback information and determines the CoMPtransmission parameters, and either performs CoMP transmission to theterminal device, cooperating with another base station, or determinesthe MIMO transmission parameters, referring to the MIMO feedbackinformation, and performs MIMO transmission (step S1414).

The positions of the reference signals for MIMO, which is a basictransmission mode, are notified by the base station to the terminaldevice beforehand, and when the transmission mode is switched,notification is made of the feedback method instruction. Also, whenswitching to the CoMP mode, notification is made of the CoMP referencesignal positions. By doing this, it is possible to improve theefficiency of feedback-related signaling. By associating the feedbackmethod instruction with the reference signal position notification, itis possible to reduce the overhead in signaling.

By the terminal device notifying the base station of the MIMO feedbackinformation and the CoMP feedback information, it is possible for thebase station to switch between the CoMP mode and the MIMO modedynamically, so that efficient use of frequency spectrum is possible.Additionally, when the parameters are determined at the time of CoMPtransmission, because it is possible to consider the MIMO feedbackinformation, it is possible to more preferably set the transmissionparameters. For example, when determining the modulation method andcoding rate at the time of CoMP transmission, by referencing the CQI forMIMO, it is possible to more preferably use the modulation method andcoding rate.

There is no restriction to transmitting from the terminal device to thebase station with the same timing for the MIMO feedback information andthe CoMP feedback information at step S1413. For example, even in thecase in which reporting is done of the CoMP feedback information and theMIMO feedback information using different subframes, it is possible toachieve the same type of effect as noted above. Also, the MIMO feedbackinformation at step S1413 is not necessarily the same as the MIMOfeedback information at step S1403. For example, the MIMO feedbackinformation at step S1413 may be a part of the MIMO feedback informationat step S1403. More specifically, the MIMO feedback information at stepS1413 may be information indicating the broadband quality, with the MIMOfeedback information at step S1403 indicating the broadband quality(status) and the narrowband quality (status). In this case as well, itis possible to achieve the effect as noted above.

The description of the present embodiment was for the case in which aCoMP mode terminal device reports not only CoMP feedback but also MIMOfeedback to the base station based on the second embodiment. In theother above-described embodiments, in the case in which a CoMP modeterminal device reports MIMO feedback, in addition to CoMP feedback, tothe base station, the same effect as noted above can be achieved.

Seventh Embodiment

In the first embodiment or in the second embodiment, the description wasfor the case in which wireless frames are synchronized between cellscapable of CoMP (subframes having the same number of subframes areplaced at the same times). In the seventh embodiment according to thepresent invention, the case in which wireless frames are notsynchronized will be described.

Because the configurations of a base station and a terminal device inthe seventh embodiment are the same as those of the base station (FIG.7) and the terminal device (FIG. 8) in the first embodiment, theirdetailed descriptions will be omitted herein.

The present embodiment will be described below, with references made tothe drawings.

FIG. 15A and FIG. 15B are drawings showing examples of the configurationof the reference signals that are referenced by the terminal device thatperforms CoMP. In the present embodiment, the description is for a cellconfiguration that is similar to that shown in FIG. 1 and FIG. 2.

A resource block 1501 as shown in FIG. 15A is transmitted from the basestation 101 that covers the cell #1, this being a resource block thatincludes the MIMO reference signal at the cell #1.

A resource block 1502 as shown in FIG. 15B is transmitted from the basestation 102 that covers the cell #2, this being a resource block thatincludes the CoMP reference signal that is transmitted from the cell #2at the same time as the resource block that includes the MIMO referencesignal at the cell #1.

Resource elements 1501-1 to 1501-4 within the resource block 1501 areresource elements onto which LTE-A reference signals are mapped. Theresource element 1501-6 indicates a resource element that punctures. Theresource element 1501-6 is a resource element in the cell #1 having thesame frequency and the same time as a resource element with which theCoMP reference signal is transmitted from the cell #2. The otherresource element 901-5 indicates a resource element onto which a signalother than an LTE-A reference signal (that is, a data signal, a controlsignal, an LTE reference signal, a reference signal for modulation, orthe like) is mapped. In contrast, the resource elements 1502-1 to 1502-4within the resource block 1501 indicate resource elements onto whichLTE-A CoMP reference signals are mapped. The other resource element1502-5 is a resource element onto which a signal other than an LTE-Areference signal (that is, a data signal, a control signal, an LTEreference signal, a reference signal for modulation, or the like) ismapped.

As shown in FIGS. 15A and 15B, definition is made such that the resourceelement mapping MIMO reference signal and the resource element mappingCoMP reference signal are different resource elements. By doing this,because MIMO reference signal of the local cell and CoMP referencesignal of the local cell or another cell can be placed within the samesubframe, reference signal placement is possible with a high degree offreedom.

FIG. 16 is a drawing showing an example of the configuration of wirelessframes transmitted from the base station 101 and the base station 102.In FIG. 16, the horizontal axis represents time. A wireless frame 1601shown as signal 1 in FIG. 16 is transmitted from the base station 101that covers the cell #1. A wireless frame 1602 shown as signal 2 in FIG.16 is transmitted from the base station 102 that covers the cell #2.Each of the wireless frames includes 10 subframes SF#0 to SF#9. Thisdrawing shows the case in which the wireless frames are offset by 5subframes between cells.

The subframes 1601-2 and 1602-2 are subframes in which MIMO referencesignals for MIMO communication in the cell #1 and the cell #2 areplaced, respectively. The subframes 1601-3 and 1602-3 are subframes inwhich CoMP reference signals in the cell #1 and the cell #2 are placed,respectively. The subframes 1601-2 and 1602-4 are subframes that aretransmitted in the same time with the subframes 1602-3 and 1601-3. Forthis reason, puncturing is done in the resource elements onto which theCoMP reference signals are mapped. For example, in the subframe 1601-2,a subframe in which the resource block 1501 in FIG. 15A is placed can beused. The other subframes 1601-1 and 1602-1 are normal subframes.

As described above, the terminal device 104 in FIG. 1 can measure theCoMP reference signal at the cell #1 in the subframe SF#6 with highaccuracy. In the same manner, it can measure the CoMP reference signalat the cell #2 in the subframe SF#2 with high accuracy.

In this manner, the base station does not perform puncturing for thefirst reference signal that is referenced by a terminal device that doesnot perform CoMP. In contrast, the base station performs puncturing forthe second reference signal that is referenced by a terminal device thatperforms CoMP, and places the first reference signal and the secondreference signal into different subframes. By doing this, the terminaldevice can generate highly accurate feedback information.

Also, in the above-described each embodiment, although the descriptionhas been presented using the resource element or the resource block asthe mapping unit for reference signals, and using the subframe or thewireless frame as the transmission unit in the time direction, this isnot restriction. Alternatively, even if the region and the time unitthat are configured by arbitrary frequency and time are used, the sameeffect can be achieved.

Furthermore, each of the above-described embodiments has been describedfor the case in which notification for instruction of MIMO feedback fromthe base station or for instruction of CoMP feedback is made to theterminal device. These instructions are for instructing the threeprocess steps of measuring for MIMO or CoMP, generating of feedbackinformation for MIMO or CoMP, and reporting of feedback information forMIMO or CoMP. By performing the three process steps using one signaling(or by renewing a parameter at the same timing), the efficient signalingis possible.

Alternatively, the three process steps may be instructed using differenttiming or signaling. By doing this, flexible instruction can beachieved, thereby enabling improvement of performance of communicationwith respect to signaling processing. For example, notifications of aCoMP measurement and of a CoMP feedback information generation are madeusing different timing or signaling from the base station to theterminal device, thereby enabling flexible setting of a cell group to bemeasured and a cell group in which feedback information is to begenerated.

Also, although the above described each embodiment has been presentedfor the cases in which switching from the initial mode to the MIMO modeand from the MIMO mode to the CoMP mode are done, this is notrestriction. For example, in the cases in which switching from theinitial mode to the CoMP mode is done and then transferring from theCoMP mode to the MIMO mode is done, the same scheme can be used and canachieve the same effect.

Alternatively, a program for the purpose of implementing all or part ofthe function of the base station in FIG. 7 and all or part of thefunction of the terminal device in FIG. 8 may be recorded on acomputer-readable recording medium, and a computer system may read andexecute the program recorded on the record medium, thereby performingthe various part processing. The term “computer system” includes anoperating system and also hardware, such as peripheral devices.

The term “computer system” also includes a webpage-providing environment(or display environment) if the WWW system is used.

The term “computer-readable medium” refers to a portable medium, such asa flexible disk, an optical-magnetic disc, a ROM, and a CD-ROM, and astorage device, such as a hard disk, that is built into a computersystem. The term “computer-readable medium” includes something thatdynamically retains a program for a short time, for example, acommunication line when the program is transmitted via a network such asthe Internet, a communication line such as a telephone line, or thelike, as well as a medium to retain a program for a certain time, forexample, a flash memory internally provided in a computer system actingas the server and client in that case. The program may have the objectof implementing a part of the above-described function, and it may alsoimplement the above-described function in combination with a programalready stored in a computer system.

Alternatively, implementation of all or part of the function of the basestation in FIG. 7 and all or part of the function of the terminal devicein FIG. 8 may be done by incorporation into an integrated circuit.

Although the embodiments of the present invention are described abovewith references made to the accompanying drawings, the specificconfiguration is not limited to the embodiments, and various designs,changes and the like are encompassed within the scope thereof, withoutdeparting from the present invention.

INDUSTRIAL APPLICABILITY

The present invention is preferable for use as a wireless transmitterapparatus, a wireless receiver apparatus, a wireless communicationsystem, and a wireless communication method.

REFERENCE SYMBOLS

-   -   101, 102, 201: Transmitter apparatus    -   103, 104: Receiver apparatus    -   301, 302, 303, 401, 402, 403, 901, 902, 903, 1501, 1502:        Resource block    -   301-1 to 301-5, 302-1 to 302-5, 303-1 to 303-5, 401-1 to 401-6,        402-1 to 402-6, 403-1 to 403-6, 901-1 to 301-5, 902-1, 902-2,        903-1, 903-2, 1501-1 to 1501-6, 1502-1 to 1502-5: Resource        element    -   501, 502, 503, 1001, 1002, 1003, 1601, 1602: Wireless frame    -   501-1 to 501-3, 502-1 to 502-3, 503-1 to 503-3, 1001-1 to        1001-4, 1002-1 to 1002-4, 1003-1 to 1003-4, 1601-1 to 1601-3,        1602-1 to 1602-4: Subframe    -   701-1, 701-2: Coding unit    -   702-1, 702-2: Scrambling unit    -   703-1, 703-2: Modulating unit    -   704: Layer mapping unit    -   705: Precoding unit    -   706: Reference signal generating unit    -   707-1, 707-2: Resource element mapping unit    -   708-1, 708-2: OFDM signal generating unit    -   709-1, 709-2: Transmitting antenna    -   710: Receiving antenna    -   711: Received signal processing unit    -   712: Feedback information processing unit    -   713: Higher layer    -   801-1, 801-2: Receiving antenna    -   802-1, 802-2: OFDM signal demodulating unit    -   803-1, 803-2: Resource element demapping unit    -   804: Filter unit    -   805: Deprecoding unit    -   806: Layer demapping unit    -   807-1, 807-2: Demodulating unit    -   808-1, 808-2: Descrambling unit    -   809-1, 809-2: Decoding unit    -   810: Higher layer    -   811: Reference signal measuring unit    -   812: Feedback information generating unit    -   813: Transmitted signal generating unit    -   814: Transmitting antenna    -   1701, 1901, 1902: Transmitter apparatus    -   1702, 1903: Receiver apparatus    -   1801: Resource block    -   1801-1 to 1801-6: Resource element

The invention claimed is:
 1. A terminal apparatus configured and/orprogrammed to communicate with a base station apparatus configuring afirst cell, the terminal apparatus comprising: acquiring circuitryconfigured and/or programmed to acquire, from the base station apparatusby using higher layer signaling, first information, second information,third information, and fourth information, the first informationspecifying a first number indicating a first subframe, the firstsubframe including a first resource element in which a first referencesignal of the first cell is placed, the second information specifying asecond number indicating a second subframe, the second subframeincluding a second resource element in which a second reference signalof a second cell other than the first cell is to be placed, the secondresource element being not used to transmit a signal of the first cell,the third information indicating a position of the first resourceelement, and the fourth information indicating a position of the secondresource element; and demapping circuitry configured and/or programmedto demap data, wherein, in the first subframe, the data is mapped onresource elements which do not include the first resource element, inthe second subframe, the data is mapped on resource elements which donot include the second resource element, and the first subframe and thesecond subframe are in the first cell.
 2. The terminal apparatusaccording to claim 1, wherein the acquiring circuitry is configuredand/or programmed to acquire, from the base station apparatus, thirdinformation specifying the first resource element.
 3. The terminalapparatus according to claim 1, wherein the acquiring circuitry isconfigured and/or programmed to acquire, from the base stationapparatus, fourth information specifying the second resource element. 4.A base station apparatus configured and/or programmed to configure afirst cell and to communicate with a terminal apparatus, the basestation apparatus comprising: notifying circuitry configured and/orprogrammed to notify, by using higher layer signaling, the terminalapparatus of first information, second information, third information,and fourth information, the first information specifying a first numberindicating a first subframe, the first subframe including a firstresource element in which a first reference signal of the first cell isplaced, the second information specifying a second number indicating asecond subframe, the second subframe including a second resource elementin which a second reference signal of a second cell other than the firstcell is to be placed, the second resource element being not used totransmit a signal of the first cell, the third information indicating aposition of the first resource element, and the fourth informationindicating a position of the second resource element; and mappingcircuitry configured and/or programmed not to map data onto the firstresource element, when the data is mapped onto resource elementsincluded in the first subframe, and not to map data onto the secondresource element, when the data is mapped onto resource elementsincluded in the second subframe, in the first subframe, the data ismapped on resource elements which do not include the first resourceelement, and the first subframe and the second subframe are in the firstcell.
 5. The base station apparatus according to claim 4, wherein thenotifying circuitry is configured and/or programmed to notify theterminal apparatus of third information specifying the first resourceelement.
 6. The base station apparatus according to claim 4, wherein thenotifying circuitry is configured and/or programmed to notify theterminal apparatus of fourth information specifying the second resourceelement.
 7. A method performed by a terminal apparatus communicatingwith a base station apparatus configuring a first cell, the methodcomprising: acquiring, from the base station apparatus by using higherlayer signaling, first information, second information, thirdinformation, and fourth information, the first information specifying afirst number indicating a first subframe, the first subframe including afirst resource element in which a first reference signal of the firstcell is placed, the second information specifying a second numberindicating a second subframe, the second subframe including a secondresource element in which a second reference signal of a second cellother than the first cell is to be placed, the second resource elementbeing not used to transmit a signal of the first cell, the thirdinformation indicating a position of the first resource element, and thefourth information indicating a position of the second resource element;and demapping data, wherein in the first subframe, the data is mapped onresource elements which do not include the first resource element, inthe second subframe, the data is mapped on resource elements which donot include the second resource element, and the first subframe and thesecond subframe are in the first cell.
 8. A method performed by a basestation apparatus configuring a first cell and communicating with aterminal apparatus, the method comprising: notifying, by using higherlayer signaling, the terminal apparatus of first information, secondinformation, third information, and fourth information, the firstinformation specifying a first number indicating a first subframe, thefirst subframe including a first resource element in which a firstreference signal of the first cell is placed, the second informationspecifying a second number indicating a second subframe, the secondsubframe including a second resource element in which a second referencesignal of a second cell other than the first cell is to be placed, thesecond resource element being not used to transmit a signal of the firstcell, the third information indicating a position of the first resourceelement, and the fourth information indicating a position of the secondresource element; not mapping data onto the first resource element, whenthe data is mapped onto resource elements included in the firstsubframe; and not mapping data onto the second resource element, whenthe data is mapped onto resource elements included in the secondsubframe in the first subframe, the data is mapped on resource elementswhich do not include the first resource element, and, the first subframeand the second subframe are in the first cell.